Definition Hardware

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These electronic circuits, along with the memory and input/output devices, form the computer's hardware. Hardware consists of tangible objects - integrated circuits, printed circuit boards, cables, power supplies, memories, and printers - rather than abstract ideas, algorithms, or instructions.
Software, in contrast, consists of algorithms (detailed instrucions telling how to do something) and their computer representations - namely, programs. Programs can be stored on hard disk, floppy disk, CD-ROM, or other media, but the essence of software is the set of instructions that makes up the programs, not the physical media on which they are recorded.
In the very first computers, the boundary between hardware and software was crystal clear. Over time, however, it has blurred considerably, primarily due to the addition, removal, and merging of levels as computers heave evolved. Nowadays, it is often hard to tell them apart (Vahid, 2003). In fact, a central theme of this book is

Hardware and software are logically equivalent.

Any operation performed by software can also be built directly into the hardware, preferably after it is sufficently well understood. As Karen Panetta Lentz put it: "Hardware is just petrified software." Of course, the reverse is also true: any instruciton executed by the hardware can also be simulated in software.
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